Contactless Interface for mm-wave Near Field Communication

ABSTRACT

A system is provided in which a first waveguide has a first resonator coupled to an end of the first waveguide. A second waveguide has a second resonator coupled to the second waveguide. The first resonator is spaced apart from the second resonator by a gap distance. Transmission of a signal propagated by the first waveguide across the gap to the second waveguide is enhanced by a confined near field mode magnetic field produced by the first resonator in response to the propagating wave that is coupled to the second resonator.

FIELD OF THE INVENTION

This invention generally relates to the use of near field communication(NFC) in place of physical/ohmic contacts for communication among systemmodules.

BACKGROUND OF THE INVENTION

In electromagnetic and communications engineering, the term waveguidemay refer to any linear structure that conveys electromagnetic wavesbetween its endpoints. The original and most common meaning is a hollowmetal pipe used to carry radio waves. This type of waveguide is used asa transmission medium for such purposes as connecting microwavetransmitters and receivers to their antennas, in equipment such asmicrowave ovens, radar sets, satellite communications, and microwaveradio links.

A dielectric waveguide employs a solid dielectric core rather than ahollow pipe. A dielectric is an electrical insulator that can bepolarized by an applied electric field. When a dielectric is placed inan electric field, electric charges do not flow through the material asthey do in a conductor, but only slightly shift from their averageequilibrium positions causing dielectric polarization. Because ofdielectric polarization, positive charges are displaced toward the fieldand negative charges shift in the opposite direction. This creates aninternal electric field which reduces the overall field within thedielectric itself. If a dielectric is composed of weakly bondedmolecules, those molecules not only become polarized, but also reorientso that their symmetry axis aligns to the field. While the term“insulator” implies low electrical conduction, “dielectric” is typicallyused to describe materials with a high polarizability; which isexpressed by a number called the dielectric constant (∈k) and/or by anumber called the relative permittivity (∈r). The term insulator isgenerally used to indicate electrical obstruction while the termdielectric is used to indicate the energy storing capacity of thematerial by means of polarization.

The electromagnetic waves in a metal-pipe waveguide may be imagined astravelling down the guide in a zig-zag path, being repeatedly reflectedbetween opposite walls of the guide. For the particular case of arectangular waveguide, it is possible to base an exact analysis on thisview. Propagation in a dielectric waveguide may be viewed in the sameway, with the waves confined to the dielectric by total internalreflection at its surface.

Near Field Communication (NFC) is a wireless technology allowing twodevices to communicate over a short distance of approximately 10 cm orless. Various protocols using NFC have been standardized internationallywithin NFC Forum specifications and defined in ISO/IEC 18092, ECMA-340,and ISO 14443, for example. NFC allows a mobile device to interact witha subscriber's immediate environment. With close-range contactlesstechnology, mobile devices may be used as credit cards, to access publictransportation, to access secured locations, and many more applications.Contactless systems are commonly used as access control ID's (e.g.employee badges), as well as payment systems for public transportationetc. More recently, credit cards are beginning to include NFCcapability.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the invention will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIGS. 1-2 are side views of a system illustrating near field couplingacross a gap between two waveguides with the aid of resonators;

FIGS. 3A-3C, 4 illustrate an exemplary waveguide coupler and resonatorplaced in the waveguides of FIGS. 1-2 in more detail;

FIGS. 5-7 are plots illustrating simulated operation of the system ofFIGS. 1-2;

FIG. 8 is a block diagram of an example system that uses waveguides withresonators for NFC communication between modules;

FIG. 9 is a more detailed illustration of modules for the system of FIG.8;

FIG. 10 is a pictorial illustration of the example system of FIG. 8;

FIG. 11 is a flow chart illustrating operation of near fieldcommunication (NFC) between adjacent modules;

FIG. 12 is a cross sectional view of another embodiment of a systemusing near field coupling across a gap; and

FIGS. 13-15 illustrate other embodiments of systems using resonators toimprove coupling efficiency of NFC across a gap between waveguides.

Other features of the present embodiments will be apparent from theaccompanying drawings and from the detailed description that follows.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Specific embodiments of the invention will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency. In thefollowing detailed description of embodiments of the invention, numerousspecific details are set forth in order to provide a more thoroughunderstanding of the invention. However, it will be apparent to one ofordinary skill in the art that the invention may be practiced withoutthese specific details. In other instances, well-known features have notbeen described in detail to avoid unnecessarily complicating thedescription.

As frequencies in electronic components and systems increase, thewavelength decreases in a corresponding manner. For example, manycomputer processors now operate in the gigahertz realm. As operatingfrequencies increase to sub-terahertz, the wavelengths become shortenough that signal lines that exceed a short distance may act as anantenna and signal radiation may occur. For example, in a material witha low dielectric constant of 3, such as a printed circuit board, a 100GHz signal will have a wavelength of approximately 1.7 mm. Thus, asignal line that is only 1.7 mm in length may act as a full wave antennaand radiate a significant percentage of the signal energy in thematerial.

Waves in open space propagate in all directions, as spherical waves. Inthis way, in the far-field regime, they lose their power proportionallyto the square of the distance; that is, at a distance R from the source,the power is the source power divided by R². Such random wavepropagation may also result in interference to other systems that arelocated nearby and be in violation of emission limits set by standardbodies such as FCC and IEC.

A wave guide may be used to transport high frequency signals overrelatively long distances. The waveguide confines the wave topropagation in one dimension, so that under ideal conditions the waveloses no power while propagating. Electromagnetic wave propagation alongthe axis of the waveguide is described by the wave equation, which isderived from Maxwell's equations, and where the wavelength depends uponthe structure of the waveguide, and the material within it (air,plastic, vacuum, etc.), as well as on the frequency of the wave.Commonly-used waveguides are only of a few categories. The most commonkind of waveguide is one that has a rectangular cross-section, one thatis usually not square. It is common for the long side of thiscross-section to be twice as long as its short side. These are usefulfor carrying electromagnetic waves that are horizontally or verticallypolarized.

For the exceedingly small wavelengths encountered for sub-THz radiofrequency (RF) signals, dielectric waveguides perform well and are muchless expensive to fabricate than hollow metal waveguides. Furthermore, ametallic waveguide has a frequency cutoff determined by the size of thewaveguide. Below the cutoff frequency there is no propagation of theelectromagnetic field. Dielectric waveguides have a wider range ofoperation without a fixed cutoff point.

Using NFC coupling with waveguides to distribute signals between variousmodules may provide a low cost interconnect solution. Embodiments ofthis disclosure may provide a way to interface removable system moduleswithout using physical/ohmic contacts.

FIGS. 1-2 are side views of a portion of an example system 100illustrating near field communication (NFC) across a gap 104 between twowaveguides 110, 111 with the aid of resonators 112, 113. In thisexample, substrate 101 may contain or be coupled to high frequencycircuitry that is configured to generate a radio frequency (RF) signal.In some embodiments, the RF signal may have a fundamental frequency inthe range of approximately 10-200 GHz, for example. The substrate 101may be a printed circuit board (PCB) implemented using any commonly usedor later developed material used for electronic systems and packages,such as: fiberglass, plastic, silicon, ceramic, Plexiglas, etc., forexample.

A waveguide 110 may be located adjacent substrate 101 and extend for adistance D1 away from substrate 101. As discussed above, waveguide 110may be a metallic waveguide, a dielectric waveguide, a dielectric filledmetallic waveguide, or other known or later developed transmission mediafor propagation of RF signals. A coupler 114 may be fabricated onsubstrate 101 for launching the RF signal into waveguide 110. Coupler114 may be a shorted loop of a microstrip, for example, that isconnected to the circuitry that generates the RF signal. In anotherembodiment, coupler 114 may be a differential loop in which a microstripon each side is fed differentially. Other embodiments may use otherknown or later developed structures for launching an RF signal intowaveguide 110.

Similarly, another substrate 102 may contain or be coupled to highfrequency circuitry that is configured to receive an RF signal. In someembodiments, the RF signal may have a fundamental frequency in the rangeof approximately 10-200 GHz, for example. The substrate 102 may be a PCBimplemented using any commonly used or later developed material used forelectronic systems and packages, such as: fiberglass, plastic, silicon,ceramic, Plexiglas, etc., for example.

A waveguide 111 may be located adjacent substrate 102 and extend for adistance D2 away from substrate 102. As discussed above, waveguide 111may be a metallic waveguide, a dielectric waveguide, a dielectric filledmetallic waveguide, or other known or later developed transmission mediafor propagation of RF signals. A coupler 115 may be fabricated onsubstrate 102 for receiving the RF signal from waveguide 110. Coupler115 may be a shorted loop of a microstrip, for example, that isconnected to the circuitry that receives the RF signal. In anotherembodiment, coupler 114 may be a differential loop in which a microstripon each side is fed differentially. Other embodiments may use otherknown or later developed structures for receiving an RF signal fromwaveguide 111.

A resonator 112 may be fabricated on the end of waveguide 110 oppositefrom coupler 114, as will be described in more detail below. Similarly,a resonator 113 may be fabricated on an end of waveguide 111 oppositecoupler 115. In this example, the end of waveguide 110 containingresonator 112 is spaced apart from the end of waveguide 111 containingresonator 113 by a gap distance 104. The gap may simply be a spacebetween the two ends and be filled with air, for example. In someembodiments, there may be a solid material 103 filling all or a portionof gap 104. Solid material 103 may be a dielectric or insulatingmaterial, such as plastic, glass, fiberglass, ceramic, Plexiglas, etc.

Distance D1, D2 may be relatively short for applications in which thesubstrates are packaged within system modules that are located closetogether, examples of which will be disclosed below. In otherapplications, D1 and/or D2 may be long when substrate 101 is located alonger distance from substrate 102. For example, substrate 101 may beseparated from substrate 102 by several inches, several feet, or evenhundreds of feet or more. Waveguides 110, 111 allow signal confinementand propagation with low loss over long distances.

FIG. 2 illustrates the operation of NFC in system 100. Launch structure114 may be a shorted loop of microstrip or a differential loop, forexample, that creates a magnetic field 202 in waveguide 110 to match theTE01 mode H-field of waveguide 110. This allows for transitioning from amicrostrip propagation mode to a waveguide propagation mode. H-field 202then induces a propagating E-field 203 according to waveguidepropagation principles. When propagating E-field 203 interacts withresonator 112, a current is generated that produces confined near fieldmode magnetic field 205. Confined near field mode magnetic field 205 isessentially a non-radiating evanescent field that magnetically coupleswith resonator 113 across gap 104 to produce an induced current inresonator 113. The induced current in resonator 113 then creates amagnetic field 206 that induces propagating E-field 207 in waveguide111. When E-field 207 reaches coupler 115, a magnetic field 208generates an RF signal that may then be routed to receiver circuitry onsubstrate 102.

In this manner, an RF signal may be transferred from circuitry onsubstrate 101 to circuitry on substrate 102 via waveguides 110, 111across gap 104 with minimal loss or radiation to adjacentsystems/components due to a confined near field mode magnetic fieldproduced by resonator at the end of each waveguide adjacent the gap.

FIGS. 3A-3C, 4 illustrate an exemplary coupler and resonator placed inthe waveguides of FIGS. 1-2 in more detail. FIG. 3B is an end viewlooking into waveguide 310 through substrate 301. The description heremay be applied to both of waveguides 110, 111 in FIG. 1-2. FIG. 3Aillustrates an example IC 320 that may contain RF circuitry that isconnected to waveguide coupler 314. IC 320 may include receivercircuitry for processing an RF signal received on coupler 314 viawaveguide 310 or transmitter circuitry for producing an RF signal thatis transmitted by coupler 314 into waveguide 310. In some embodiments,IC 320 may contain both transmitter circuitry and receiver circuitry,for example.

Coupler 314 may be a discrete loop that is soldered to substrate 301,for example. Coupler 314 may be a differential loop which has amicrostrip 321 on each side to feed it differentially, as illustrated inFIG. 3B. In FIG. 3A, copper trace 321 is configured as a microstrip overground plane 322. FIG. 3C illustrates another implementation in whichone side of the loop 314 may be shorted 323 to ground for a single-endedfeed.

Referring now to FIG. 3B, resonator 312 is essentially an open loop thatis configured to interact with a propagating wave on the waveguide towhich it is mounted. Resonator 312 may be fabricated on a single layersubstrate and attached to the end of waveguide 310, for example, usingknown or later developed techniques, such as: an adhesive, by solderingmounting pads on the substrate to the metal waveguide, etc. In someembodiments, waveguide 310 may have a dielectric core. In this case,resonator 312 may be formed on the end of the dielectric core using anadditive process such as inkjet printing using conductive ink, forexample. In another embodiment, resonator 312 may be mounted on adielectric such as dielectric 103 (referring again to FIG. 1) that isadjacent to the end of waveguide 310.

FIG. 4 is an isometric view of coupler 112 and 113 illustrating how thecouplers may be oriented with respect to each other and spaced apart bygap 104.

FIG. 5 is a filed strength plot illustrating simulated operation of thesystem of FIGS. 1-2. In this example, E-field 203 is propagating throughwaveguide 110 in a direction indicated by vector 502. When E-field 203encounters resonator 112, a strong confined near field mode magneticfield is produced that magnetically couples across gap 104 to resonator113 without significant loss or radiation to nearby systems/components.The confined field acts as an evanescent field that does not radiate.

FIG. 6 is a plot illustrating coupling efficiency versus gap distance,measured in the wavelength of the propagating signal. Plot line 602illustrates a system without resonators, while plot line 604 illustratesoperation of a system with resonators placed at the ends of thewaveguides on either side of a gap. Notice that an efficiencyimprovement of approximately 1 dB may be observed for a gap of 0.35wavelength with the use of resonators, for example. As discussed above,for a frequency of 100 GHz, the wavelength is approximately 1.7 mm in amaterial with a dielectric constant of 3.

FIG. 7 is a plot illustrating coupling efficiency versus frequency. Plotline 702 illustrates a system without resonators, while plot line 704illustrates operation of a system with resonators placed at the ends ofthe waveguides on either side of a gap. In this example, the waveguideis configured to have propagation mode 1 starting at 100 GHz, andpropagation mode 2 starting at 200 GHz. In this case, coupled resonatorsinserted into the gap are designed to have a limited bandwidth and mayincrease the coupling efficiency over a selected band of frequencies.

In another embodiment, several resonators tuned for different ranges offrequencies may be inserted to increase the bandwidth. In anotherembodiment, wide band resonators may be used to increase the bandwidth.

FIG. 8 is a block diagram of an exemplary system that uses waveguideswith resonators for NFC communication between modules. System 800 is anexample programmable logic controller that uses guided NFC communicationbetween modules. A programmable logic controller (PLC), or programmablecontroller, is a digital computer used for automation of typicallyindustrial electromechanical processes, such as control of machinery onfactory assembly lines, amusement rides, light fixtures, etc. PLCs areused in many machines, in many industries. PLCs are designed formultiple arrangements of digital and analog inputs and outputs, extendedtemperature ranges, immunity to electrical noise, and resistance tovibration and impact. Programs to control machine operation aretypically stored in battery-backed-up or non-volatile memory. A PLC isan example of a “hard” real-time system since output results must beproduced in response to input conditions within a limited time,otherwise unintended operation will result. PLC systems are well knownand need not be described in detail herein; e.g. see: “ProgrammableLogic Controller”, Wikipedia, as of Dec. 1, 2015, which is incorporatedby reference herein.

In this example, there are several modules that will be referred to as“line cards”. Various types of line cards may be installed in a chassisor rack and configured for various purposes, such as: to controlmanufacturing processes, to control the heating and cooling in abuilding, to control medical equipment, etc. As such, electricalisolation is often needed or desirable to prevent ground loops or otherinteractions between various pieces of equipment that are beingcontrolled. In the past, various types of isolation devices have beenused, such as: optical isolators, transformers, etc.

In this example, there is a power supply line card 802, a datacommunication line card 810, and several processing line cards 820, 840,841. While five line card modules are illustrated in FIG. 8, a typicalchassis may accommodate ten or more modules. While a system using linecards is illustrated herein, embodiments of the disclosure are notlimited to line cards. Various types of modules may make use of thecommunication techniques explained herein in order to provide reliablecommunication between removable modules.

In this example, supply line card 802 is coupled to a source of powerand in-turn may produce one or more voltages that may be distributed viaa bus 804 that may be coupled to each of the line cards via connectorssuch as connector 805. Typically, voltage bus(es) 804 may be included ina backplane that provides support for the connectors 805.

Data communication line card 810 may be configured to send and receivedata via a communication channel to a remote host or another rack orchassis, for example. Various types of communication line card 810 mayaccommodate a wireless or wired interface. For example, an internetconnection to a local or a wide area net may be provided by line card810. Alternatively, a wireless connection to a Wi-Fi network or to acellular network may be provided by line card 810.

Processing line card 820 may include, front end interface logic 830,processing logic 831, and aggregator logic 832, for example. Front endinterface logic 830 may be of various types to provide interconnectionto equipment that is being controlled, such as: input and outputsignals, RS232/422/485 compatible signals, digital signals, analogsignals, etc. Various types of logic may be provided, such as: analog todigital converters (ADC), digital to analog converters (DAC), relays,contacts, etc. Processing logic 831 may include various types ofhardwired and programmable logic, microcontrollers, microprocessors,memory, etc. Line cards 840, 841, etc may be identical or similar toline card 820 and may include various types and combinations ofprocessing and interface logic as needed for a given control task.

In this example, each line card is configured to allow it to communicatewith its nearest neighbor on both sides. For example, line card 810 maytransmit via transmitter 811 to line card 820 which has a receiver 824.Similarly, line card 820 may transmit via transmitter 823 to receiver815 on line card 810. At the same time, line card 820 may transmit viatransmitter 822 to adjacent line card 840 and receive via receiver 821from adjacent line card 840.

In a similar manner, each line card in system 800 may communicate witheach other line card in a daisy chain manner. Each line card includes anaggregator/de-aggregator logic function, such as 832 on line card 820,that allows each line card to recognize communication on the daisy chainintended for it. The aggregator/de-aggregator function also allows aline card to originate a communication packet that is then provided tothe daisy chain and then propagated through adjacent line cards to afinal destination on a target line card. In this embodiment, the daisychain operates in a similar manner to an internet network protocol andeach aggregator 832 functions as an internet interface. In anotherembodiment, a different type of known or later developed peer to peerprotocol may be used.

As mentioned above, NFC may be used as the transport vehicle tocommunicate between each adjacent line card. As will be described inmore detail below, waveguide segments, such as waveguide 815, 825 and816, 826 may be used to guide the NFC between each adjacent line cardmodule in order to minimize signal spreading and interface to othersystems and devices.

FIG. 9 is a more detailed illustration of modules for the system of FIG.8. FIG. 9 illustrates two example line card modules 921, 922 that arerepresentative of the various modules 810, 820, 840, etc of system 800.Module 921 may include a substrate 901 on which are mounted variouscircuit components, such as an integrated circuit (IC) 951 that includestransmitter(s) and receivers(s), such as transmitter 823 and receiver824 and/or transmitter 822 and receiver 821, of line card 820, forexample. In some embodiments, there may be a separate IC for eachtransmitter and receiver. In another embodiment, one or more receiversand transmitters may be formed in a single IC, for example. Similarly,module 922 may include substrate 902 on which are mounted variouscircuit components, such as an integrated circuit (IC) 952 that includestransmitter(s) and receivers(s), for example.

Integrated circuits 951, 952 may also include aggregation logic,processing logic and front end logic, or there may be additional ICsmounted on substrate 901, 902 that contain aggregation logic, processinglogic, and front end logic. Substrate 901 may be a single or amultilayer printed circuit board, for example. IC 951 and other ICs maybe mounted on substrate 901 using through hole or surface mounttechnology using solder bumps or bonding depending on the frequency ofoperation, or other known or later developed packaging technologies.Substrate 901, 902 may be any commonly used or later developed materialused for electronic systems and packages, such as: fiberglass, plastic,silicon, ceramic, Plexiglas, etc., for example.

Substrates 901, 902 may also contain a waveguide (WG) coupler 914 thatis connected to the receiver and/or transmitter that is contained withinIC 951. WG coupler 915 may also be coupled to the receiver and/ortransmitter that are contained within IC 951, 952. WG coupler 914, 915may be similar to couplers 314, referring back to FIGS. 3A-3B. Thecouplers may be separate structures that are mounted on substrate 901,or they may be embedded within substrate 901.

A waveguide 910 may be mounted in a position that places itapproximately centered over WG coupler 914. Similarly, a waveguide 911may be mounted in a position that places it approximately centered overWG coupler 915. In this manner, a majority of the electromagnetic energythat is emanated by WG coupler 914 will be captured and confined bywaveguide 910 and thereby directed to an adjacent module with minimalexternal radiation and signal loss.

As described in more detail above, a resonator may be fitted in the endof waveguides 910, 911 in order to convert a propagating wave in eachwaveguide to/from a confined near field mode evanescent magnetic fieldaround the resonator to allow NFC across gap distance 904. Embodimentsof the disclosure may operate in near field mode in which the separationbetween adjacent modules is a fraction of the wavelength of thefrequency being transmitted by the transmitter(s) in IC 951. Forexample, transmission frequencies in a range of 100 GHz to 200 GHz maybe used. However, some embodiments may use frequencies that are higheror lower than this range. A 100 GHz signal will have a wavelength ofapproximately 3 mm in air.

A shield 963 may be provided between left WG coupler 915 and right WGcoupler 914 to minimize “back scatter” of the field produced by each WGcoupler. Shield 963 may be a conductive layer, for example, that isconnected to a ground reference for the module. Shield 963 is spacedapart from each coupler 914, 915 by a distance greater than lambda/10,where lambda is the wavelength of the signal being emitted by thecouplers, in order to avoid capacitance effects that may reduce thebandwidth of the coupler. For example, the wavelength of a 30 GHz signalin a dielectric having an ER of 1 is approximately 10.0 mm. In thisexample, substrate 901 is a typical PWB material that has an ∈_(R) ofapproximately 1.0. Therefore, as long as the shield is spaced away fromeach coupler by a distance 973 of at least 1 mm, then capacitanceeffects should be minimized in a system operating at 30 GHz. Lowerfrequency operation may require larger spacing.

Near field mode may produce an evanescent field that may be used tocouple two adjacent resonators 912, 913. Evanescent fields by natureexhibit an exponential decay with distance away from the source. Byvirtue of near proximity between resonator 912 of module 921 and anotherresonator 913 in an adjacent module 922 that is only a few mm's away, areasonable TX-to-RX signal coupling may be achieved using the evanescentfield in near field mode while mitigating emission limits/concernsoutlined per FCC Part 15.

The best analogy would be that of a transformer. A strong self-couplingbetween coils results in reduced leakage to the external world.Furthermore, any leakage may be considered un-intentional. Therequirements for un-intentional radiation per FCC is greatly relaxedcompared to those for intentional emissions.

Module 921 may be enclosed in a housing that is roughly indicated at961, 961. One side of the housing is illustrated as panel 961 while theother side as panel 962, which may be metal or plastic, for example.Typically, the housing will be a few mm thick.

Waveguide 910 may be a dielectric block, for example. Electromagneticwave propagation through the dielectric block may be described by thewave equation, which is derived from Maxwell's equations, and where thewavelength depends upon the structure of the dielectric block, and thematerial within it (air, plastic, vacuum, etc.), as well as on thefrequency of the wave. Waveguide 910, 911 may be able to confine thefield emitted by WG coupler by having a permittivity and/or permeabilitythat is significantly greater than surrounding materials and/or airwhich will significantly reduce the wavelength of the electromagneticfield emitted by WG coupler 914. Similarly, waveguide 910, 911 may beable to confine the field emitted by WG coupler by having a permittivityand/or permeability that is significantly lower than surroundingmaterials and/or air which will significantly increase the wavelength ofthe electromagnetic field emitted by WG coupler 914. Alternatively,waveguide 910, 911 may be constructed from a metamaterial that causes asignificant reduction or increase in wavelength of the electromagneticfield emitted by WG coupler 914.

For example, waveguide 910, 911 may be a dielectric block that has arelative permittivity greater than approximately 2.0. Similarly,waveguide 910, 911 may be a dielectric block that has a relativepermeability less than approximately 2.0.

In another embodiment, dielectric waveguide 910 may have a conductivelayer around the periphery to further confine and direct anelectromagnetic field radiated by WG coupler 914. The conductive layermay use a metallic or non-metallic conductive material to form sidewallsaround waveguide 910, 911, such as: metals such as copper, silver, gold,etc., a conductive polymer formed by ionic doping, carbon and graphitebased compounds, conductive oxides, etc., for example.

Depending on the material and thickness of module wall 961, waveguide910 may be simply mounted to be adjacent to an inside surface of modulewall 961 such that the radiated signal passes through module wall 961.In some embodiments, a window may be provided in module wall 961 so thatan outer surface of waveguide 910 may be positioned flush, slightlyindented, or slightly proud of an outside surface of module wall 961,for example. The general location on the surface of the housing wherethe waveguide is located will be referred to herein as a “port”.

FIG. 9 also illustrates a portion of a second module 922 that may belocated adjacent module 921. Module 922 may have a housing that includesa panel 962, that will be referred to as a “left” panel. Module 921 mayhave a panel 961 that will be referred to as a “right” panel. Module 922may include a substrate 902 that holds various ICs, such as IC 952 thatmay include a receiver and transmitter, and a WG coupler 914, 915.Module 922 may also include a waveguide 911 that is positioned adjacentleft panel 962 and in alignment with WG 910 in module 921.

When module 921 and module 922 are installed in a chassis, right panel961 will be in close proximity to left panel 962, as indicated at 904.Waveguide 910 of module 921 and waveguide 911 of module 922 areconfigured so that they are in approximate alignment with each other. Inthis manner, a signal that is generated by a transmitter in IC 951 maybe provided to coupler 914, radiated into waveguide 910 and therebydirected to resonator 912 and then received by resonator 913 of module922, launched into waveguide 911, received by coupler 914 on substrate902 and thereby provided to a receiver in IC 952.

Module 921 or 922 may be easily removed from or inserted into a chassiswithout any wear and tear on contacts that were previously required tocommunicate signals between modules. Furthermore, NFC using resonators912, 913 provide complete electrical isolation between module 921 andmodule 922. An additional isolation mechanism is not required.

FIG. 10 is a pictorial illustration of an exemplary system 1000 that isanother view of system 800 of FIG. 8. Backplane 1006 provides a set ofconnectors 1005 for providing power to each line card, as explained withregard to connector 105 of FIG. 1. As can be seen by the illustration,each line card module is removable from backplane 1006 by simply pullingthe module to disconnect it from connector 1005. Typically, a rack orchassis will also be provided along with backplane 1006 to support theline cards when they are inserted into connectors 1005.

Each line card module is enclosed in a housing, which may be made fromplastic or other suitable materials. As described in more detail above,each line card may have a WG coupler, waveguide and resonator arrangedto form a contactless communication port on each side of the module. Forexample, module 1010 may have a port 1055 on the right side of themodule while module 1020 may have a port 1056 on the left side of themodule that aligns with port 1055 when both modules are plugged intobackplane 1006.

Similarly, module 1020 may have another port (not shown) on the rightside of the module while module 1040 may have a port (not shown) on theleft side of the module that aligns when both modules are plugged intobackplane 1006. All of the modules may have similar pairs of ports onboth sides of each module to allow daisy chained communication among allof the modules, as described in more detail above.

FIG. 11 is a flow chart illustrating operation of near fieldcommunication between modules, as described above in more detail. Asdescribed above in more detail, the modules may be part of aprogrammable logic control system used for industrial, commercial, andresidential applications. A typical system may include a rack or chassisinto which a set of modules are installed. Each module may communicatewith an adjacent neighbor module using near field communication, inwhich an RF signal generated in one module may be EM coupled to areceiver in an adjacent module using radiative coupling, near fieldcoupling, or evanescent coupling, or any combination of these modes.

For example, a radio frequency (RF) signal may be generated 1102 in afirst module. In the example of FIGS. 1-10, the RF signal may have afrequency in the range of 100-200 GHz. However, other systems may use RFsignals at a higher or lower frequency by adjusting the physical size ofthe field coupling and field confining components described herein.

An RF electromagnetic field may be emanated 1104 in response to the RFsignal from a first waveguide coupler in the first module. The RFelectromagnetic field may be the result of a traveling wave formed in amicrostrip loop, for example, as described in more detail with regard toFIGS. 3A-3B.

The emanated RF electromagnetic field is confined and directed 1106 by awaveguide in the first module to a resonator at the end of thewaveguide. A confined near field mode magnetic evanescent field may begenerated by the resonator in response to the propagatingelectromagnetic field in the waveguide.

The evanescent field may inductively couple 1108 to a similar resonatorlocated at the end of a waveguide in an adjacent second module. Asdescribed in more detail above, the two resonators are located in closeproximity when the modules are installed in a system and therebyminimize loss of emanated energy to the surroundings. As described abovein more detail, this coupling is performed by EM coupling and may usethe near field of the emanated electromagnetic field from the resonator.The coupling may also make use of an evanescent field that is formed bythe first WG coupler. There may also be some portion of the propagatingfield from the waveguide in the first module that radiates across thegap between modules. Depending on the spacing between the adjacentmodules, one or the other or a combination of these coupling modes mayoccur. This may simplify the process of complying with FCC emissionrequirements, for example.

The emanated RF electromagnetic field is then propagated 1110 to asecond WG coupler in the second module.

A resultant RF signal may then be provided 1112 to an RF receiver on thesecond module. As described above in more detail, the multiple modulesin the system may communicate in a daisy chained manner such that anymodule may be able to communicate with any other module in the system.

A known standard communication protocol, such as the Internet Protocol(IP) may be used, treating the daisy chained NFC physical media as anEthernet. The Internet Protocol (IP) is the principal communicationsprotocol in the Internet protocol suite for relaying datagrams acrossnetwork boundaries. IP has the task of delivering packets from thesource host to the destination host solely based on the IP addresses inthe packet headers. For this purpose, IP defines packet structures thatencapsulate the data to be delivered. It also defines addressing methodsthat are used to label the datagram with source and destinationinformation. The first major version of IP, Internet Protocol Version 4(IPv4), is the dominant protocol of the Internet. Its successor isInternet Protocol Version 6 (IPv6).

Another embodiment may use another known or later developedcommunication protocol for communication using the daisy chained NFCphysical media as described herein.

In this manner, embodiments of the present disclosure may provide highthroughput communication between removable modules of a system usingnear field communication techniques. The techniques described herein maybe less expensive than alternatives such as optical couplers, forexample. NFC allows contactless communication between modules andthereby eliminates the need for additional isolation in systems that mayrequire isolation between modules.

FIG. 12 is a cross sectional view of another embodiment of a portion ofa system 1200 using near field coupling across a gap 1204. In thisexample, a substrate 1201 has a waveguide 1210 formed within thesubstrate. Substrate 1201 may be a printed circuit board (PCB)implemented using any commonly used or later developed material used forelectronic systems and packages, such as: fiberglass, plastic, silicon,ceramic, Plexiglas, etc., for example. An integrated circuit 1220 may bemounted on substrate 1201 and be coupled to waveguide 1210 using acoupler similar to coupler 314 as illustrated in FIG. 3A, for example.Other examples of waveguides formed in a substrate and coupled to an ICare described in U.S. Pat. No. 9,306,263, “Interface Between anIntegrated Circuit and a Dielectric Waveguide Using a Dipole Antenna anda Reflector”, Juan Herbsommer et al. and is incorporated by referenceherein.

A second waveguide 1211 may be configured to interface to waveguide1210. As described above in more detail, a resonator 1212 placed in theend of waveguide 1211 and an adjacent resonator placed in an end ofwaveguide 1210 may improve coupling efficiency across gap 1204. In thisexample, an insulating or dielectric layer 1202 may be formed over aportion or over the entirety of substrate 1201. Layer 1202 may be formedfrom various materials, such as: silicon dioxide, glass, quartz,ceramic, plastic, etc.

FIG. 13 illustrates a portion of a system 1300 with multiple resonatorsused for larger gaps. In this example, waveguides 1310, 1311 areseparated by a larger gap 1304. As described above in more detail,resonators 1312, 1313 may be placed in the ends of waveguides 1310, 1311in order to improve coupling efficiency across gap 1304. However,referring back to FIG. 6, coupling efficiency decreases as the gap getswider. Beyond approximately a half wavelength gap the efficiency may betoo low for good results.

Installing one or more resonators 1314 spaced across a gap may allow theeffective length of the gap between each pair of resonators to bemaintained below approximately 0.5 wavelength, for example.

FIG. 14 illustrates a portion of a system 1400 in which resonators aremounted on a dielectric adjacent the end of a waveguide 1410, 1411. Asdescribed above in more detail, resonators 1412, 1413 may improvecoupling efficiency across gap 1404. In this example, resonators 1412,1413 may be applied to a surface of a dielectric 1461, 1462 that isforming all or a portion of the gap. For example, referring back to FIG.9, dielectric 1461 may represent the right panel 961 of a module whiledielectric 1462 may represent a left panel 962 of a module. In thismanner, waveguides 1410, 1411 may be simple waveguides that arepositioned adjacent resonators 1412, 1413 when each module is assembled.

FIG. 15 illustrates a portion of a system 1500 in which waveguide 1510and waveguide 1511 form a “T” intersection with a gap 1504 between them.In this example, resonators 1512, 1513 may be installed in thewaveguides to improve efficiency of coupling across gap 1504. In otherembodiments, other intersection configurations may also be improved withresonators, such as: a 90 degree bend intersection, a 45 degree bendintersection, etc.

Other Embodiments

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various other embodiments of the invention will beapparent to persons skilled in the art upon reference to thisdescription. For example, while a programmable logic controller systemwas described, other types of modular systems may embody aspects of thepresent disclosure in order to improve reliability.

While modules in which the guided NFC ports are located on the side ofthe module were described herein, in another embodiment a port may belocated on an edge of a module with a mating port located on a backplaneor other surface that is adjacent to the edge of the module, forexample.

While a daisy-chained communication configuration was described herein,in another embodiment other topologies may be formed. For example, atree topology may be formed by providing a port on the backplane thatmates with an edge mounted port in each module.

While a simple dielectric block has been described herein, anotherembodiment may use a metallic or non-metallic conductive material toform sidewalls on the waveguide field confiner, such as: a conductivepolymer formed by ionic doping, carbon and graphite based compounds,conductive oxides, etc., for example.

A dielectric or metamaterial waveguide field confiner may be fabricatedonto a surface of a substrate or module panel using an inkjet printingprocess or other 3D printing process, for example.

While dielectric waveguide field confiners with polymer dielectric coreshave been described herein, other embodiments may use other materialsfor the dielectric core, such as ceramics, glass, etc., for example.

While waveguides with a rectangular cross section are described herein,other embodiments may be easily implemented. For example, the waveguidemay have a cross section that is square, trapezoidal, cylindrical, oval,or many other selected geometries.

The dielectric core of a conductive waveguide may be selected from arange of approximately 2.4-12, for example. These values are forcommonly available polymer dielectric materials. Dielectric materialshaving higher or lower values may be used when they become available.

While sub-terahertz signals in the range of 100-200 GHz were discussedherein, WG couplers, waveguides with resonators and systems fordistributing higher or lower frequency signals may be implemented usingthe principles described herein by adjusting the physical size of thewaveguide and resonator accordingly.

Certain terms are used throughout the description and the claims torefer to particular system components. As one skilled in the art willappreciate, components in digital systems may be referred to bydifferent names and/or may be combined in ways not shown herein withoutdeparting from the described functionality. This document does notintend to distinguish between components that differ in name but notfunction. In the following discussion and in the claims, the terms“including” and “comprising” are used in an open-ended fashion, and thusshould be interpreted to mean “including, but not limited to . . . .”Also, the term “couple” and derivatives thereof are intended to mean anindirect, direct, optical, and/or wireless electrical connection. Thus,if a first device couples to a second device, that connection may bethrough a direct electrical connection, through an indirect electricalconnection via other devices and connections, through an opticalelectrical connection, and/or through a wireless electrical connection.

Although method steps may be presented and described herein in asequential fashion, one or more of the steps shown and described may beomitted, repeated, performed concurrently, and/or performed in adifferent order than the order shown in the figures and/or describedherein. Accordingly, embodiments of the invention should not beconsidered limited to the specific ordering of steps shown in thefigures and/or described herein.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the invention.

What is claimed is:
 1. A system comprising: a first waveguide having afirst resonator coupled to an end of the first waveguide; a secondwaveguide having a second resonator coupled to the second waveguide; andin which the first resonator is spaced apart from the second resonatorby a gap distance.
 2. The system of claim 1, in which the secondresonator is coupled to an end of the second waveguide.
 3. The system ofclaim 1, in which the second waveguide is aligned with the firstwaveguide in a “T” intersection configuration with the gap distancebetween them, and in which the second resonator is positioned on a sideof the second waveguide at the T intersection.
 4. The system of claim 1,in which the first waveguide and the second waveguide are metallicwaveguides.
 5. The system of claim 1, further including a one or moreadditional resonators positioned in a gap between the first resonatorand the second resonator.
 6. The system of claim 1, in which the firstresonator is a conductive open loop.
 7. The system of claim 1 in whichthe first waveguide is contained within a first module, in which thefirst module includes: a substrate on which is mounted a radio frequency(RF) circuit coupled to a first waveguide coupler located on thesubstrate; a housing that surrounds and encloses the substrate, thehousing having a first port region on a surface of the housing, in whichthe port region forms a portion of the gap distance; and in which thefirst waveguide is located between the first waveguide coupler and thefirst port region on the housing and is configured to propagatenear-field and/or evanescently coupled electromagnetic energy emanatedfrom the first waveguide coupler through the first port region.
 8. Thesystem of claim 7, in which the waveguide coupler is a shorted loop witha single end feed from the RF circuitry.
 9. The system of claim 7, inwhich the waveguide coupler is a differentially fed loop.
 10. The systemof claim 1, further including: a substrate; a dielectric layer formed onthe substrate; in which the first waveguide is positioned on thedielectric layer and in which the second waveguide is formed in thesubstrate; and in which the first resonator is positioned adjacent thesecond resonator and spaced apart by the gap distance of the dielectriclayer.
 11. The system of claim 10, in which the dielectric layer isglass.
 12. A system comprising: a first module, in which the firstmodule includes: a substrate on which is mounted a radio frequency (RF)transmitter circuit coupled to a first waveguide coupler located on thesubstrate; a housing that surrounds and encloses the substrate, thehousing having a first port region on a surface of the housing; a firstwaveguide located between the first waveguide coupler and the first portregion on the housing; and a resonator adjacent to an end of the firstwaveguide at the first port region.
 13. The module of claim 12, in whichthe first module further includes: an RF receiver mounted on thesubstrate and coupled to a second waveguide coupler located on thesubstrate; and a second waveguide located between the second waveguidecoupler and a second port region on the housing; and a second resonatoradjacent to an end of the second waveguide at the second port region.14. The system of claim 13, in which the first port region is located ona side of the housing and the second port region is located on anopposite side of the housing, such that when the first module isinstalled in the system and a second module having a third port regionis installed in the system adjacent the first module, the first portregion of the first module will align with the third port region of thesecond module.
 15. The system of claim 12, further including: abackplane with a plurality of locations for attaching a plurality ofmodules; a plurality of modules attached to the backplane, in which eachof the modules has a first port and a second port; and in which thefirst port region of each module aligns with the second port region ofan adjacent module.
 16. The system of claim 12, in which the firstresonator is attached to the inside of wall of the housing in the firstport region.
 17. A method for transmitting a signal through multiplewaveguides, the method comprising: propagating the signal through afirst waveguide in a guided wave transmission mode; converting theguided wave signal into a confined near field mode magnetic field by afirst resonator at an end of the first waveguide; magnetically couplingthe magnetic field to a second resonator at an end of a secondwaveguide, in which the second resonator is separated from the firstresonator by a gap distance; and converting the magnetic field back intoa guided wave by the second resonator such that the signal propagatesthrough the second waveguide in a guided wave transmission mode.
 18. Themethod of claim 17, in which converting the guided wave into a confinednear field mode magnetic field includes producing a circulating currentin the first transducer responsive to the guided wave.
 19. The method ofclaim 17, in which the waveguides are selected from a group consistingof metallic waveguides, dielectric waveguides, strip lines, andtransmissions lines.
 20. The method of claim 17, in which the gapdistance is filed with a material selected from a group consisting ofdielectric, air, and glass.